Variable polarization antenna



Nov. 22, 1966 J. L. KERR 3,287,730

VARIABLE POLARI ZATION ANTENNA Filed Feb. 5, 1963 FIG. I

INVENTOR, JOHN L. KERR ATTORNEY.

United States Patent 3,287,730 VARIABLE POLARIZATION ANTENNA John L. Kerr, Neptune, N.J., assignor to the United States of America as represented by the Secretary of the Army Filed Feb. 5, 1963, Ser. No. 256,481 4 Claims. (Cl. 343-756) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment of any royalty thereon.

The present invention relates to a variable polarization antenna, and more particularly to an antenna which can transmit or receive electromagnetic radiation of any desired polarization.

In the field of security communications, it has been the general practice to employ variable polarization antennas to perform the task of continuously changing the polarization of the transmitted signal according to some predetermined code. Although the prior art devices have served the purpose, they have not proved entirely satisfactory under all conditions of service for the reason that considerable difiiculty has been experienced in receiving signals whose polarization will abruptly change from one type of polarization to another. Such prior art devices have also required the removal or insertion of various elements such as dielectrics, plugs, waveguides, etc. to vary the polarization of the transmitted wave. It may be further noted that such prior art antennas have also been narrow band when propagating linearly polarized signals as a result of the geometry of such devices.

The general purpose of this invention is to provide an antenna which embraces all the advantages of similarly employed devices and possesses none of the aforedescribed disadvantages. To attain this, the invention contemplates a unique rotatable phase-shifting waveguide in the transmission line of the antenna.

An object of the present invention is the provision of a variable polarization antenna which does not require the removal or insertion of any elements to change from one type polarization to another.

Another object is to provide a variable polarization antenna which is relatively broad band when transmitting or receiving linearly polarized waves.

A further object of the invention is the provision of a variable polarization antenna which does not require dielectrics or plugs and therefore does not substantially attenuate signals of millimeter wave lengths.

Still another object is to provide an inherently matched transmission line for the radiating element of an antenna.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein:

FIGURE 1 shows a plan view of a preferred embodiment of the invention.

FIGURE 2 shows a section of the device taken on the line 2-2 of FIGURE 1 looking in the direction of the arrows.

FIGURE 3 shows a section of the device taken on the line 33 of FIGURE 1 looking in the direction of the arrows.

FIGURE 4 shows a section of the device taken on the line 44 of FIGURE 1 looking in the direction of the arrows.

FIGURES 5 and 6 show a section of the device similar to FIGURE 4 but with the waveguide rotated.

Referring now to the drawings, wherein like reference characters designate like or corresponding parts through- "ice out the several views, there is shown in FIGURE 1, which illustrates a preferred embodiment, an antenna having a radiating horn 11 and a transmission system 12 made up of three waveguides 13, 14 and 15. Waveguide 13 is made up of a conventional rectangular waveguide section 16 and a cylindrical waveguide section 17 disposed at right angles to section 16. Waveguide 13 is connected to the rotatable waveguide 14 by a conventional ball bearing choke joint 18. Waveguide 14 comprises a cylindrical section 19, and a curved rectangular section 21 whose longitudinal axis smoothly curves from a plane at right angles to section 19 to a position where the longitudinal axis of sections 19 and 21 are coincident. Waveguide 14 further comprises a second cylindrical section 22 connected by a smooth transition to section 21. A second conventional ball bearing choke joint 23 connects waveguide 14 with cylindrical waveguide 15 while a third similar choke joint 26 connects waveguide 15 with the horn 11. Cylindrical waveguide 15 comprises an elliptical squeeze section 25. Waveguides 14 and 15 are also provided with motor and gearing means 30 and 31 respectively for rotating the waveguides. Also provided are discs 34 and 35 which may contain markings for indicating the relative angular position of waveguides 14 and 15.

The operation of the device may best be understood with reference to FIGURES 2 to 6. Let it be assumed that it is desired to transmit an electromagnetic radio wave from horn 11 in the TE mode. To propagate energy in the TE mode, linearly polarized energy may be fed to waveguide section 16 in the TE mode. This energy will then be guided to horn 11, by the waveguide sections shown, in the following modes; sections 17 and 19, TE mode; section 21, TE mode; section 22, TE mode; waveguide 15 and horn 11, TE mode. The manner in which this is done is well known and will be discussed here. However, the polarization of this radiated energy as stated above will depend on the orientation of the waveguides 14 and 15 with respect to each other. The energy in the various sections may be represented by an electric vector E which will be oriented as shown in FIGURES 2 to 6. In section 21 the electric vector B will be parallel to the shorter dimension A as shown in FIGURE 2. The electric vector E in section 22 will be oriented as shown in FIGURE 3 is. parallel to the E vector in section 21. This energy is then fed to the waveguide 15 which contains the elliptical squeeze section 25. The electric vector E may best be analyzed in section 25 by resolving the vector E into two components E and E oriented along the major and minor axes of the elliptical section 25. Since the components E and E see different transverse dimensions (C and D) of the waveguide section 25, their guide wavelengths will differ and their longitudinal velocities, along the section 25, will be different, thereby causing a change in phase between these components. The values of these components E and E will depend upon the orientation of the input vector E with respect to the axes of the elliptical section 25. To find the distribution of the two components E and E of the electric vector E across the waveguide section 25, Maxwells curl equations may be solved in elliptical coordinates. When this is done, the components are found in terms of Mathieu functions. The Mathieu functions which arise are of two types, even and odd. The even mode represents the distribution of the component E and the odd mode represents the distribution of the component E Therefore, in section 25 there will be two orthoginal TE modes produflie. even and odd. The two components E and E will, as stated above, travel through section 25 with different longitudinal velocities. These velocities are measured to determine the longitudinal distances traveled by components E and E and then section 25 is terminated at that point where the components E and E are 90 out of phase. The resulting polarization will then depend on the relative values of E and E These rela tive values may be varied by merely changing the orientation of the input vector E with respect to the axes of the section 25 as shown in FIGS. 4-6. To prevent attenuation of one component more than the other, the ratio of the major axis to the minor axis of the elliptical section 25 is made as close to unity as possible while the length of section 25 is kept at a minimum consistent with the requirements for a 90 phase shift as explained above. With an elliptical ratio approaching unity the vector E will be resolved approximately into the two components E and E as shown in FIGS. 5 and 6. Actually vector E will be slightly longer while E will be shorter. However, for ease in analyzing the operation the vector is resolved as shown.

In FIG. 4 the input vector E is fed to section 25 along its minor axis D. In this case component E is zero and E is equal to E. Therefore, since component E is the only vector present there can be no change in phase and there will be no change in the polarization of the energy fed to section 25. In this case since the input energy is linearly polarized the radiated energy will also be linearly polarized. In FIG. 5, however, the input vector E is oriented at a 45 angle with respect to the major axes of section 25 and the vectors E and E are equal in magnitude. Since E will be 90 ahead of E when it leaves section 25 circular polarization will be produced. Actually E is only approximately equal to E in this case and circular polarization is produced at some angle which is very close to 45. As stated above, this angle will depend on how close to unity one can make the elliptical ratio of section 25 and still get a 90 phase shift with a reasonable length for section 25. When input vector E is between 0 and 45 with respect to the axis of section 25 the components E and E will be diiferent in magnitude and the 90 phase shift between these components will produce elliptical polarization.

For the case of linear polarization i.e. with the input vector E oriented along either the major or minor axis of section 25, the plane of polarization may be varied by rotating waveguide 14 and 15 synchronously. One may therefor produce linear polarization in any plane or rotating linear polarization. In the case of elliptical polarization if waveguides 14 and 15 are rotated together, rotating elliptical polarization will be produced. By rotating both sections 14 and 15 relative to each other the emitted radiation will change smoothly from linear polarization to elliptical to circular and so on. In both the cases of elliptical and circular polarization the resulting radiated electric vector will rotate at an angular velocity equal to the signal frequency.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. Apparatus for transforming stationary plane polarized radiation into radiation having any preselected condition of polarization comprising first and second rectangular waveguides, a circular Waveguide rotating joint coupling said first and second rectangular waveguide adjacent one end of each said rectangular waveguides, the longitudinal axis of said joint being perpendicular to the longitudinal axis of said first and second rectangular waveguides adjacent said one end, the longitudinal axis of said second rectangular waveguide at the other end being coincident with said longitudinal axis of said joint, means for rotating said second rectangular waveguide about said longitudinal axis at said other end thereof, an elliptical waveguide, a rotating joint connecting one end of said elliptical waveguide to said other end of said second rectangular waveguide with the longitudinal axis of said elliptical waveguide coincident with the longitudinal axis of said other end of said second rectangular waveguide, and means for rotating said elliptical waveguide about said longitudinal axis thereof.

2. Apparatus according to claim 1 and wherein the ratio of the major axis to the minor axis of said elliptical waveguide is close to unity.

3. Apparatus according to claim 2 and wherein the length of said elliptical section is such that radiation components polarized approximately along said major and minor axes of said elliptical waveguide will have a phase shift of ninety degrees after passing through said elliptical waveguide.

4. The apparatus according to claim 3 further including a conical horn radiating means coupled to the other end of said elliptical Waveguide.

References Cited by the Examiner UNITED STATES PATENTS 2,607,849 8/1952 Purcell et al 333-21 2,930,040 3/1960 Weil 343756 2,933,731 4/1960 Foster 343---756 3,024,463 3/ 1962 Moeller et al 333-21 3,076,188 1/1963 Schneider 343-756 3,089,104 5/1963 Allen 343 1 HERMAN KARL SAALBACH, Primary Examiner. E, LIEBERMAN, Assistant Examiner, 

1. APPARATUS FOR TRANSFORMING STATIONARY PLANE POLARIZED RADIATION INTO RADIATION HAVING ANY PRESELECTED CONDITION OF POLARIZATION COMPRISING FIRST AND SECOND RECTANGULAR WAVEGUIDES, A CIRCULAR WAVEGUIDE ROTATING JOINT COUPLING SAID FIRST AND SECOND RECTANGULAR WAVEGUIDE ADJACENT ONE END OF EACH SAID RECTANGULAR WAVEGUIDES, THE LONGITUDINAL AXIS OF SAID JOINT BEING PERPENDICULAR TO THE LONGITUDINAL AXIS OF SAID FIRST AND SECOND RECTANGULAR WAVEGUIDES ADJACENT SQID ONE END, THE LONGITUDINAL AXIS OF SAID SECOND RECTANGULAR WAVEGUIDE AT THE OTHER END BEING COINCIDENT WITH SAID LONGITUDINAL AXIS OF SAID JOINT, MEANS FOR ROTATING SAID SECOND RECTANGULAR WAVEGUIDE ABOUT SAID LONGITUDINAL AXIS AT SAID OTHER END THEREOF, AN ELLIPTICAL WAVEGUIDE, A ROTATING JOINT CONNECTING ONE END OF SAID ELLIPTICAL WAVEGUIDE TO SAID OTHER END OF SAID SECOND RECTANGULAR WAVEGUIDE WITH THE LONGITUDINAL AXIS OF SAID ELLIPTICAL WAVEGUIDE COINCIDENT WITH THE LONGITUDINAL AXIS OF SAID OTHER END OF SAID SECOND RECTANGULAR WAVEGUIDE, AND MEANS FOR ROTATING SAID ELLIPTICAL WAVEGUIDE ABOUT SAID LONGITUDINAL AXIS THEREOF. 